In general, to transmit the rotation of a vehicle transmission to a measuring device such as a speedometer, a rotation device including a flexible shaft inserted through a tubular sheath is used.
Previously, in this kind of rotation coupling device, the clearance between the flexible shaft and the liner of the tubular sheath had to be kept as small as possible in order to suppress the noise of rotation knocking sound and the vibration of the speedometer needle that occurs due to stationary wave vibrations.
However, this technique has the following disadvantages.
1. It is difficult to control the inner diameter of the tubular sheath liner so as to minimize the clearance. PA1 2. Changes of the inner diameter of the liner, when bending occurs, increase the resistance to sliding of the rotating shaft, which in turn shortens the lifetime of the rotating shaft. PA1 3. The amount of lubricant that can be injected inside the tubular sheath is reduced, which also shortens the lifetime of the rotating shaft. PA1 4. It is hard for the shaft to bend, which makes the positioning of the tubular sheath difficult.